1. Field of the Invention
Published, European Patent Application EP 0 602 258 A discloses a method for producing printed circuit boards having coarse conductor structures, in which case, however, a delimited region of the printed circuit boards is intended to obtain a very high wiring density. This is achieved by an additional wiring layer which is applied only in the delimited region and is connected to the underlying wiring layer via plated-through holes.
Published, European Patent Application EP 0 062 300 A discloses a method for producing printed circuit boards in which a metallic etching resist that has been applied over the whole area of a metal layer is selectively removed again by laser radiation in the regions which do not correspond to the conductor structures, and the conductor structures are formed by etching away the metal layer that is uncovered in this way.
International Patent Disclosure WO 00/04750 discloses a method for producing printed circuit boards having coarse conductor structures and at least one region having fine conductor structures in which the coarse conductor structures and the fine conductor structures are etched out of a metal layer in a common etching process. During the common etching process, an etching resist patterned by photolithography is used in the region of the coarse conductor structures and an etching resist patterned with the aid of a laser beam is used in the region of the fine conductor structures. In accordance with a first embodiment of the known method, a photoresist is applied to the metal layer and patterned by photolithography in such a way that, in the region of the coarse conductor structures, it has a negative pattern of the coarse conductor structures, and that it covers the entire region of the fine conductor structures. In the region of the fine conductor structures, the photoresist is then patterned with the aid of a laser beam in such a way that it has the negative pattern of the fine conductor structures. The etching resist is then applied to the coarse and fine conductor structures for example by the externally electroless deposition of tin in one work operation, so that the common etching process can be carried out after the removal of the photoresist. In accordance with a second embodiment of the known method, the photoresist applied to the metal layer is patterned by photolithography in such a way that, in the region of the coarse conductor structures, it has a negative pattern of the coarse conductor structures. The etching resist is then applied to the coarse conductor structures and to the entire region of the fine conductor structures. After the removal of the photoresist, the etching resist is then patterned in the region of the fine conductor structures with the aid of the laser beam in such a way that it has the pattern of the fine conductor structures. The coarse conductor structures and the fine conductor structures are then once again produced in a common etching process.
It is accordingly an object of the invention to provide a method for producing wiring configurations having coarse conductor structures and at least one region having fine conductor structures which overcomes the above-mentioned disadvantages of the prior art methods of this general type, in such a way that it can be carried out in a shorter time.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for producing wiring configurations. The method includes providing an electrically insulating substrate, applying a metal layer to the electrically insulating substrate, applying an etching resist to the metal layer, applying a photoresist to the etching resist, patterning the photoresist using photolithography such that a pattern of coarse conductor structures and a region of fine conductor structures are covered, removing the etching resist in regions not covered by the photoresist, removing the photoresist, patterning the etching resist with a laser beam such that it has a pattern of the fine conductor structures, and etching away those regions of the metal layer which are not protected by the etching resist as far as a surface of the electrically insulating substrate in a common etching process to form the coarse conductor structures and the fine conductor structures.
The invention is based on the insight that, by combining conventional photoetching technology for producing the coarse conductor structures and the laser patterning for producing the fine conductor structures, in each case large regions of the photoresist, of the etching resist and of the metal layer can be rapidly removed by the steps of exposing and developing the photoresist, stripping the etching resist and etching the metal layer. Since the laser patterning of the etching resist in the region of the fine conductor structures can be carried out rapidly in any case, the result is that overall minimal time is taken.
Although, in principle, organic resists can also be used as the etching resist, a metallic etching resist is preferred. The application of the metallic etching resist to the metal layer can then be performed rapidly and with little outlay by externally electroless or electrical metal deposition. In this case, the use of tin or tin-led as etching resist has proved particularly successful.
It is possible to produce plated-through holes both in the region of the coarse conductor structures and in the region of the fine conductor structures.
In accordance with an added mode of the invention, there is the step of applying the photoresist such that openings of the plated-through holes are covered with the photoresist.
If the etching resist disturbs the further treatment of the wiring configuration, it is removed again. In this case, it is then possible for example to apply other metal layers to the coarse and to the fine conductor structures.
In a refinement of the invention, it is possible, in a simple manner, to produce wiring configurations having two or else having a plurality of wiring layers which in turn have coarse and fine conductor structures.
In accordance with a concomitant mode of the invention, there are the step of forming a first wiring layer from the coarse conductor structures and/or the fine conductor structures on the electrically insulating substrate, applying a further electrically insulating substrate to the first wiring layer, forming further through holes in the further electrically insulating substrate, applying a further metal layer to the further electrically insulating substrate including the further through holes resulting in further plated-through holes, applying a further etching resist to the further metal layer, applying a further photoresist to the further etching resist, patterning the further photoresist using photolithography such that a pattern of further coarse conductor structures and a region of further fine conductor structures are covered, removing the further etching resist in regions not covered by the further photoresist, removing the further photoresist, patterning the further etching resist with the laser beam such that it has the pattern of the further fine conductor structures, etching away those regions of the further metal layer which are not protected by the further etching resist as far as a surface of the further electrically insulating substrate in a further common etching process to form the further coarse conductor structures and the further fine conductor structures, and forming a second wiring layer from the further coarse conductor structures and the further fine conductor structures.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for producing wiring configurations having coarse conductor structures and at least one region having fine conductor structures, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.